611
FXUS10 KWNH 311851
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
151 PM EST TUE DEC 31 2019
VALID DEC 31/1200 UTC THRU JAN 04/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH FINAL PREFERENCES/CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..LOW DEPARTING FROM NEW ENGLAND TODAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.
..CLOSED LOW ENTERING MEXICO AND WEAKENING WEDNESDAY NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/UKMET/CMC BLEND
CONFIDENCE: AVERAGE
TIMING DIFFERENCES ARE STILL APPARENT AS A CLOSED LOW ENTERS
MEXICO ON WEDNESDAY, WITH THE 12Z NAM AND 12Z ECMWF SLOWEST WHILE
THE 12Z GFS AND 00Z ECMWF ARE SLIGHTLY FASTER. TRENDS IN THE
ENSEMBLE SPAGHETTI PLOTS OF 500 MB HEIGHTS SHOW A SUDDEN SLOWING
VALID 00Z/04 AFTER WHAT HAD BEEN FAIRLY CONSISTENT TIMING FROM
CYCLE TO CYCLE. THE 12Z ECMWF/UKMET/CMC ARE CONSISTENT WITH THE
00Z/31 ENSEMBLE CYCLE TREND TO BE SLOWER, WHICH WARRANTS A SHIFT
TOWARD THAT TREND. A NUDGE SLOWER THAN THE PRELIMINARY PREFERENCE
IS RECOMMENDED, WHICH CONSTITUTES A BLEND OF THE FASTER 12Z GFS
AND SLOWER 12Z UKMET/CMC.
...ATMOSPHERIC RIVER INTO PAC NW TODAY AND AMPLIFYING LONGWAVE
TROUGH ACROSS THE CENTRAL U.S. THURSDAY EVENING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/UKMET/CMC BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE
A LONGWAVE TROUGH DEVELOPS OVER THE GREAT PLAINS THURSDAY INTO
FRIDAY WITH MODEL DIFFERENCES WITH THE EVOLUTION OF SHORTWAVES
WITHIN. THE 12Z NAM STANDS OUT THE GREATEST WITH A MORE POSITIVE
TILT TO THE SOUTHERN PORTION OF THE MID-LEVEL TROUGH AXIS BY
FRIDAY EVENING. A SLOWER TREND IN THE 12Z ECMWF IS A MOVE TOWARD
THE 12Z NAM BUT LESS EXTREME. MEANWHILE THE 12Z UKMET/CMC ALSO
TRENDED A BIT SLOWER/DEEPER WITH THE LONGWAVE TROUGH MAKING THE
12Z GFS STAND OUT FROM THE DETERMINISTIC GUIDANCE. REGARDING AN
850 MB LOW WHICH IS EXPECTED TO TRACK FROM THE SOUTHERN PLAINS
INTO THE MIDWEST, SOMEWHERE BETWEEN THE 12Z GFS, 12Z CMC AND 12Z
UKMET IS PREFERRED WHICH PLACES A SURFACE LOW ALONG THE IN/OH
BORDER AT 00Z/04.
...SHORTWAVE TROUGH AND SURFACE LOW APPROACHING PACIFIC NORTHWEST
FRIDAY/SATURDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NEAR THE 12Z NAM
CONFIDENCE: SLIGHTLY BELOW AVERAGE
THE ENSEMBLES SHOW A FAIR DEGREE OF SPREAD WITH THE TIMING OF THE
NEXT SHORTWAVE TO NEAR THE PACIFIC NORTHWEST BY THE WEEKEND.
UPSTREAM FLOW BECOMES ZONAL OVER THE CENTRAL PACIFIC WHICH WOULD
IMPLY A FASTER PROGRESSION DOWNSTREAM INTO THE PACIFIC NORTHWEST.
INDEED, TRENDS HAVE BEEN FASTER IN THE ENSEMBLE SPAGHETTI HEIGHT
PLOTS OVER THEIR PAST 4 00Z/12Z CYCLES AND IN THE 12Z UKMET/CMC
WITH A SIMILAR 12Z ECMWF TO ITS 00Z CYCLE. HOWEVER, CAUTION IS
ADVISED WITH THE FASTEST AND OFTEN BIASED GFS WHICH IS OUT AHEAD
OF THE GEFS/ECMWF/CMC ENSEMBLE MEMBERS. THE 12Z NAM APPEARS TO BE
A BETTER FIT WHICH IS TOWARD THE FASTER SIDE OF THE DETERMINISTIC
GUIDANCE BUT NOT AS SLOW AS THE 12Z ECMWF/UKMET.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
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